In offset printing machines, ink is dispensed from an ink reservoir and transferred via a vibrating roller to a plurality of inking applicator rollers onto the printing plate mounted on the printing cylinder. One or more of the ink applicator rollers are ink distributing rollers which are adapted for axial transverse movement during the printing operation.
The drive for the distributing rollers may, for example, be in the form of a gear which transforms rotary movement of a gear wheel connected to the plate cylinder to a crank mechanism which has an adjustable stroke and is adaptable for effecting corresponding reciprocating movement of the distributing roller, such as shown in EP 0 000 329 Al, and DD-PS 113 718. Alternatively, cam drives, such as shown in DE 3 424 721 C2, or gears with tumble disks, may be used to effect reciprocating axial displacement of the distributing roller. The stroke as well as the reversal point of the axial movement is adjustable by such drive mechanisms to correspond with the printing requirements and desired ink densities.
In offset printing machines, in the event of a faulty sheet engagement or other malfunction, the paper inflow into the printing machine must be stopped and the last sheet must be allowed to run through the machine. Simultaneously, the ink applicator rolls must be shut off from the plate cylinder and movement of the vibrator roller interrupted. During such stoppage, the speed of the printing machine automatically can be reduced. During the print-free operation when paper is not being run through the printing machine, however, the inking mechanism, by reason of the large number of splitting processes in the ink flow path, continues to effect a balancing of the ink layer thicknesses in both the printing direction and the transverse direction. After resumption of the printing operation, i.e., after proper paper inflow and the corresponding switching in of the switched off elements, a large number of sheets must be run through the printing machine before the proper layer thickness distribution of the inking rollers can be reestablished to the level prior to the stoppage, resulting in considerable waste.
In order to reduce the amount of spoiled sheets after such stoppage, inking mechanisms are known which have so-called ink stream separation. Ink stream separation means that during the "Print Off" operating mode when the printing press is operating without paper passing through the machine, the ink flow in the inking mechanism is interrupted at certain places where inking rollers are separated from one another. The ink layer thickness balancing then only occurs within a reduced number of inking mechanisms. Such ink stream separation is described, for example, in "Technologie des Offsetdruckes" (Technology of offset printing), VEB Fachbucherverlag Leipzin 1989, page 223 ff. Depending upon where the ink separation occurs, ink layer thickness variations still occurs.